The Colour of Justice is the most vital piece of theatre on the London stage. This dramatisation of the Stephen Lawrence inquiry can't help but serve as a rallying cry, but it is more than a clarion call. Richard Norton-Taylor, who has condensed more than 11,000 pages of transcripts, and Nicholas Kent, who directs superbly, have distilled and focused the material, throwing significant moments into sharp relief. But it has not been shaped into a traditional courtroom drama - there is, after all, no conclusion.

It is said that those conducting the inquiry found their Establishment scepticism about institutional racism altered in the face of the evidence. Audiences are also likely to have their minds changed. In scrutinising the conduct of this investigation, it illuminates the different - at times scarcely visible - faces of prejudice.

"There are," one of the police witnesses observes, "subtleties around corruption. As there are around racism." Not the remark of an unreflective plod. And those subtleties are on display here. Was the policeman who said that he had never heard a racist remark in 14 years' service with the police deaf, lying or lucky? Why did one officer think that Doreen Lawrence was not capable of spontaneously querying procedures but must have been primed to ask questions? What enabled the assured condescension of the policewoman who explained that, having spent her childhood in Africa, "I understand black people."

The opinions and tendencies of the youths who were widely and shrewdly suspected of having committed the murder have been extensively reported: they went around with knives stuffed down their trousers; they were videoed declaring that "niggers should be cut up and left with stumps". The police errors and sloppiness - the insufficient surveillance, the failure to follow up information - have been well catalogued. Nevertheless, hearing this evidence live is to be forcibly struck by certain aspects, in particular the stubbornness, complacency and obfuscation of certain police statements: "I certainly think I would have kept copies," hedged one officer who said he couldn't find his relevant notes but did know where his clipboard was.

None of this would be so powerful were the staging more histrionic. A background of constant humdrum activity accompanies even the most gruelling evidence: people chew, tap pencils, drop sheets of paper. The performances are taut and exceptionally natural. As Michael Mansfield, counsel for the Lawrence family, Jeremy Clyde swoops from sardonic loftiness to lethal snap. Christopher Fox is a convincing, confident thug.

There is also a memorable appearance by Tim Woodward as Conor Taaffe, who was in Eltham on the night of Stephen Lawrence's murder. He saw two youths running along the road and knew immediately that something was wrong. He watched one fall and he went to help. His wife had cradled the boy's head in her lap and told him: "You are loved." Taaffe's own shirt was stained with blood and when he washed it the next day, he took the water and poured it on a rose bush in his garden. This thoughtful witness was also one of the most truthful. Asked whether he had at first thought that those two running black youths might be up to no good, he said yes; when one of them stumbled, he had thought it might be a ploy.